Most prior-art methods for dispensing volatile air-freshening liquids--e.g. by pulling a portion of a long, fibrous wick from a container that is filled with a highly diluted liquid, or spraying the liquid from an aerosol can--are limited to uses in which the liquids are applied for rather brief, incremental periods. The rapid evaporation of the liquids used in these methods, and the unequal rates of evaporation of their constituents, prevent the methods from maintaining adequately uniform air freshening over long periods of time.
Many persons have recognized and sought to satisfy a need for longer-term air-freshening. Solid air-treating gels comprising a fragrant volatilizable substance, large amounts of water, and a gelling agent (see Turner et al, U.S. Pat. No. 2,691,615, issued in 1954) are one such attempt. But even these gels do not maintain uniform air freshening, as indicated by the suggestion in Turner et al that the gel be segmented so as to provide fresh surfaces for evaporation at later stages in use of the gel.
Others have proposed more elaborate arrangements, but without achieving widespread utility. For example, Hoek et al, U.S. Pat. No. 3,770,199, teaches a dispensing device that comprises a porous tubular member, with pores so fine that the member holds the liquid to be dispensed, and an impermeable tubular member telescoped around the porous member. Besides being rather complicated in structure, this device is limited in the kind of liquids that can be dispensed and the situations in which it can be used, since vaporization must occur within the tubular member and the vapors then transmitted through the walls of the tubular member.
Another example is Gray, U.S. Pat. No. 3,550,853, which seeks to provide controlled release of volatiles by wicking liquid through a resilient polyurethane open-cell foam compressed to a predetermined extent. However, the lack of uniformity in pore size, the comparatively low level of connection between cells, and the variation in the nature of the foam over a period of use limits uniformity in release of vapor.